# Arefeva-Faddeev-Slavnov formalism The AFS formalism is a way to formulate the S-matrix using an action principle. ## Refs - original: [[1974#Arefeva, Slavnov, Faddeev]] ## Application in celestial holography - [[2023#Kim, Kraus, Monten, Myers]]: equivalence between AFS and LSZ; soft theorem from AFS - [[2023#Jain, Kundu, Minwalla, Parrikar, Prabhu, Shrivastava]]: boundary correlators and bulk point singularities